The invention relates to an air spring which includes a flexible member, which encloses an air volume, and two connecting parts. Each of the connecting parts has a clamp seat to which an end of the flexible member is attached with the aid of a clamp ring allocated to the clamp seat. The invention further relates to a method for making the air spring.
Air springs of the above-mentioned kind are known from the state of the art as disclosed, for example, in U.S. Pat. No. 4,657,229. These air springs are especially utilized in motor vehicles for resiliently suspending the vehicle body relative to at least one axle of the vehicle. The clamp ring with which the flexible member of the air spring is attached to the clamp seat of a connecting part has an axially arranged cylindrical inner side in air springs known from the state of the art. A clamp ring of this kind can be produced in a simple manner because of its simple form. However, it is noted that the outer side of the flexible member and the clamp ring clamped thereon move relative to the clamp seat when pull or thrust loads act upon the flexible member of the air spring. The clamp ring also moves in the axial direction of the air spring because of the friction connection between the flexible member and the clamp ring. In the course of time, the clamp connection of the end of the flexible member on the clamp seat can loosen as a consequence of the axial movement of the flexible member and of the clamp ring. In the extreme case, it even can happen that the end of the flexible member is pulled off the clamp seat and the air spring suddenly becomes untight. The danger that the flexible member separates from the clamp seat is especially great when the flexible member is configured to have a thick wall because then especially large shear deformations occur in the flexible member during a dynamic loading thereof which are transferred to the clamp ring.
It is an object of the invention to provide an air spring having a clamp connection which prevents, to the greatest extent possible, a dynamic separation of the flexible member from the clamp seat. It is another object of the invention to provide a method for making such an air spring which can be carried out in a simple and cost-effective manner.
The air spring of the invention includes: a flexible member enclosing an air volume and having first and second end portions; a first connecting part having a first clamp seat for accommodating the first end portion thereon; a second connecting part having a second clamp seat for accommodating the second end portion thereon; a first clamp ring for attaching the first end portion to the first clamp seat; a second clamp ring for attaching the second end portion to the second clamp seat; and, at least one of the clamp seats being configured to be at least approximately convex and the one clamp ring corresponding to the one clamp seat having an inner side all of which is at least approximately concave.
An approximately convex surface here means a convex surface as well as a surface for which the curvature of the convex surface is substituted by straight lines connected one to the other. The same applies to the concave surface.
The basic idea of the invention is that the clamp connection, which comprises the clamp ring and the clamp seat, has a component part having an at least approximately concave surface and a component part having at least an approximately convex surface. The two components mutually engage via the end of the flexible member of the air spring.
An advantage achieved with the invention is especially that a form-tight connection is provided via the flexible member of the air spring between the clamp ring and the clamp seat of the connecting part. This form-tight connection prevents the clamp ring together with the flexible member from being pulled from the clamp seat. Here, it is noted that the clamp action of the clamp ring is even increased when the flexible member tends to pull from the clamp seat because of the dynamic load. In this case, the clamp ring migrates with the flexible member in the axial direction so that the gap width between the clamp ring and the clamp seat becomes less and the clamp action is increased.
A further advantage of the invention is that the inner surface of the clamp ring is available as an additional friction surface for the flexible member because the clamp ring cannot be pulled off with the flexible member from the clamp seat in the axial direction of the air spring. This leads to a clear increase of the holding force of the flexible member on the clamp seat.
A further advantage of the invention is that the firm seat of the clamp ring on the clamp seat reduces the wear of the flexible member in the clamping region whereby the service life of the flexible member is increased. Still another advantage of the invention is that an especially thick flexible member can be clamped with the clamp connection according to the invention so that especially stable air springs can be manufactured.
According to another feature of the invention, the convex surface of the clamp seat has a peripherally extending nose or projection. The advantage of this feature is that the projection additionally increases the holding force of the end of the flexible member on the clamp seat because the projection digs into the rubber of the flexible member.
According to another feature of the invention, the projection is located in the part of the convex surface of the clamp seat which faces toward the air volume of the air spring. The advantage of this feature is that there is still an adequate length of the flexible member available rearward of the projection (that is, on the side facing away from the air volume of the air spring) into which the holding forces caused by the projection can be directed.
According to still another feature of the invention, the length of the projection or nose corresponds to approximately 20% to 40% of the thickness which the flexible member has in the region of the clamp seat having the convex surface. The advantage of this feature is that even for a dynamic load of the flexible member, the danger is not present that the projection would bore through the flexible member.
According to still another feature of the invention, the convex surface of the clamp seat has at least one peripherally extending groove in the portion thereof facing away from the air volume of the air spring. The advantage of this feature is that a greater low-temperature tightness and a greater high-temperature tightness of the air spring can be achieved with one or several peripherally extending grooves in the above-mentioned region. This is so because the rubber material of the flexible member disposed on the clamp seat penetrates into the grooves. It has been shown that the low-temperature tightness and the high-temperature tightness are especially increased when the clamp seat includes a peripherally extending projection in addition to the at least one groove because the projection fixes the end of the flexible member in its position on the clamp seat. Preferably, the grooves have a depth of 0.3 to 0.6 mm. Furthermore, the cross sections of the grooves are preferably selected to be triangular because grooves of this kind are easy to manufacture and facilitate an easy penetration of the rubber of the flexible member.
According to another feature of the invention, the inner side of the clamp ring and the convex surface of the clamp seat conjointly define, over a region thereof, a channel tapered toward the air volume of the air spring. Preferably, this channel is formed on the part of the clamp seat which is facing away from the air volume of the air spring. The advantage of this feature is that the flexible member is clamped stronger by the tapering channel than by a channel of uniform width when forces act on the flexible member which could lead to the flexible member being pulled off of the clamp seat. For the end of the flexible member, the tapering channel defines a type of bottleneck through which the end of the flexible member cannot be easily pulled through.
According to still another feature of the invention, a peripherally extending projection or nose, which faces toward the air volume of the air spring, extends from the end of the clamp seat having the convex surface. The advantage of this feature is that the reliability is increased so that the flexible member will not be pulled off the clamp seat because the flexible member becomes clamped between the clamp ring and the above-mentioned projection when there is a pull-off movement.
According to another feature of the invention, a peripherally extending flange extends from the end of the clamp seat having the convex surface facing away from the air volume of the air spring. The advantage of this feature is that the end of the flexible member can be placed at a defined position on the clamp seat during assembly of the air spring and, with the aid of the flange, the depth to which the clamp ring is pushed over is pregiven.
According to another feature of the invention, the outer side of the clamp ring is cylindrical. The advantage of this feature is that conventional clamp tools having a cylindrical inner side can be used when making the air spring to radially press the clamp ring whereby the end of the flexible member is clamped between the clamp ring and the clamp seat.
Another feature of the invention provides that the clamp ring has a constant wall thickness over its entire height. In this case, the inner side of the clamp ring is first concavely formed during the radial pressing of the clamp ring when making the air spring utilizing a suitable clamp tool. The advantage of this embodiment is that the clamp ring can be made in a simple manner, for example, from a thin-walled tube or from band material.
According to another feature of the invention, the clamp ring has an easily bendable zone at approximately half elevation. The advantage of this feature is that the clamp ring can be easily deformed by the clamp tool when making the air spring and the concave inner side can be simply formed. The bendable zone can, for example, be provided in that the outer side of the clamp ring is provided with a peripherally extending groove at about half elevation.